The present invention relates to peptide nanostructures and more specifically to peptide nanostructures encapsulating foreign materials.
Nanoscience is the science of small particles of materials and is one of the most important research frontiers in modern technology. These small particles are of interest from a fundamental point of view since they enable construction of materials and structures of well-defined properties. With the ability to precisely control material properties come new, opportunities for technological and commercial development, and applications of nanoparticles have been shown or proposed in areas as diverse as micro- and nanoelectronics, nanofluidics, coatings and paints and biotechnology.
It is well established that future development of microelectronics, magnetic recording devices and chemical sensors will be achieved by increasing the packing density of device components. Traditionally, microscopic devices have been formed from larger objects, but as these products get smaller, below the micron level, this process becomes increasingly difficult. It is therefore appreciated that the opposite approach is to be employed, essentially, the building of microscopic devices from a molecular level up, primarily via objects of nanometric dimensions. Self-assembled nanoparticles, such as nanotubes and nanospheres, allow controlled fabrication of novel nanoscopic materials and devices. Such nanostrcutures have found use in areas as diverse as micro- and nanoelectronics, nanofluidics, coatings and paints and biotechnology.
In particular, wire-like semiconducting nanostructures have attracted extensive interest over the past decade due to their great potential for addressing some basic issues about dimensionality and space confined transport phenomena as well as related applications. Wire-like semiconducting nanostructures often have distinctive properties and can be used as transparent conducting materials and gas sensors. For example, fluorine-doped tin oxide films are used in architectural glass applications because of their low emissivity for thermal infrared heat. Tin-doped indium oxide films can be used for flat panel displays due to their high electrical conductivity and high optical transparency.
In the field of magnetic recording, wire-like nanostructures can be used as magnetoresistive read transducers. It has been well known that the magnetoresistive sensors are capable of reading information from the surface of magnetic recording media at high linear densities. The magnetoresistive sensors sense magnetic signals by way of the electrical resistance change of magnetoresistive elements that varies as a function of the strength and orientation of the magnetic flux sensed by read or magnetoresistive elements. The use of nanoscale elements in such sensors significantly increases the capability of retrieving accurate information from highly dense magnetic media.
In the field of displays, much effort has been devoted to developed electrophoretic displays. Such displays use a display medium comprising a plurality of electrically charged particles suspended in a fluid. Electrodes are provided adjacent the display medium so that the charged particles can be moved through the fluid by applying an electric field to the medium. In one type of such electrophoretic display, the medium comprises a single type of particle having one optical characteristic in a fluid which has a different optical characteristic. In a second type of such electrophoretic display, the medium contains two different types of particles differing in at least one optical characteristic and in electrophoretic mobility.
The most widely used building blocks of nano-materials and nano-devices are the fullerene carbon nanotubes. Two major forms of carbon nanotubes exist, single-walled nanotubes (SWNT), which can be considered as long wrapped graphene sheets and multi walled nanotubes (MWNT) which can be considered as a collection of concentric SWNTs with different diameters.
SWNTs have a typical length to diameter ratio of about 1000 and as such are typically considered nearly one-dimensional. These nanotubes consist of two separate regions with different physical and chemical properties. A first such region is the side wall of the tube and a second region is the end cap of the tube. The end cap structure is similar to a derived from smaller fullerene, such as C60.
Since nanotubes have relatively straight and narrow channels in their cores, it was initially suggested that these cavities may be filled with foreign materials to fabricate one dimensional nanowires. Early calculations suggested that strong capillary forces exist in nanotubes, which are sufficient to hold gases and fluids inside them [Pederson (1992) Phys. Rev. Lett. 69:2689]. The first experimental proof was provided by Pederson and co-workers, who showed filling and solidification of molten leaf inside nanotubes [Pederson (1992) Phys. Rev. Lett. 69:415]. Various other examples, concerning the filling of nanotubes with metallic and ceramic materials exist in the literature [Ajayan (1993) Nature 361:392; Tsang (1994) Nature 372:416; Dujardin (1994) 265:1850].
Despite high applicability, the process of filling carbon nanotubes is difficult and inefficient. Most commonly produced carbon nanotubes, are capped at at least one end of the tube and no method for efficiently opening and filling the carbon nanotubes with foreign material is known to date. For example, nanotube ends can be opened by post oxidation treatment in an oxygen atmosphere at high temperature. The major drawback of such a procedure is that the tube ends become filled with carbonaceous debris. As a consequent, filling the open-ended tubes after post oxidation with other material has proven difficult. Another problem with carbon nanotubes synthesized in inert gas arcs is the formation of highly defective tubes containing amorphous carbon deposits on both the inside surface and outside surface of the tubes and the presence of discontinuous graphite sheets. Furthermore, since carbon nanotubes are curved, wetting may prove difficult. Finally, since the internal cavity of SWNTs is very small, filling can be done only for a very limited number of materials.
Recently, peptide building blocks have been shown to form nanotubes. Peptide nanotubes are of a special interest since they are biocompatible and can be easily chemically modified.
Peptide-based nanotubular structures have been made through stacking of cyclic D-, L-peptide subunits. These peptides self-assemble through hydrogen-bonding interactions into nanotubules, which in-turn self-assemble into ordered parallel arrays of nanotubes [Ghadiri, M. R. et al., Nature 366, 324-327 (1993); Ghadiri, M. R. et al., Nature 369, 301-304 (1994); Bong, D. T. et al., Angew. Chem. Int. Ed. 40, 988-1011 (2001)].
More recently, surfactant-like peptides that undergo spontaneous assembly to form nanotubes with a helical twist have been reported. The monomers of these surfactant peptides have distinctive polar and nonpolar portions. They are composed of 7-8 residues, approximately 2 nm in length when fully extended, and dimensionally similar to phospholipids found in cell membranes. Although the sequences of these peptides are diverse, they share a common chemical property, i.e., a hydrophobic tail and a hydrophilic head. These peptide nanotubes, like carbon and lipid nanotubes, also have a very high surface area to weight ratio. Molecular modeling of the peptide nanotubes suggests a possible structural organization [Vauthey (2002) Proc. Natl. Acad. Sci. USA 99:5355; Zhang (2002) Curr. Opin. Chem. Biol. 6:865]. Based on observation and calculation, it is proposed that the cylindrical subunits are formed from surfactant peptides that self-assemble into bilayers, where hydrophilic head groups remain exposed to the aqueous medium. Finally, the tubular arrays undergo self-assembly through non-covalent interactions that are widely found in surfactant and micelle structures and formation processes.
Peptide based bis(N-α-amido-glycyglycine)-1,7-heptane dicarboxylate molecules were also shown to be assembled into tubular structures [Matsui (2000) J. Phys. Chem. B 104:3383].
However, although at least some of the above-described peptides were shown to form open-ended nanotubes [Hartgerink (1996) J. Am. Cham. Soc. 118:43-50], these are composed of peptide building blocks, which are relatively long and as such are expensive and difficult to produce, or limited by heterogeneity of structures that are formed as bundles or networks rather than discrete nanoscale structures.
There is thus a widely recognized need for, and it would be highly advantageous to have, hollow peptide nanostructures, which are devoid of the above limitations.